By means of genetic and biochemical procedures, we plan to analyze the mechanisms controlling the formation of the biosynthetic enzymes for two amino acids in Escherichia coli, isoleucine and valine. Highest priority will be given to a correlation between changes in the attenuator (control) region of the ilvGEDA operon and the level of expression of that operon. Another project will be to determine the DNA sequence in the ilvB control region, which is also thought to be controlled by attenuation. Control of the ilvC gene by substrate will be studied by studying the interaction of upsilon, the positive control element specified by ilvY, with RNA polymerase or with DNA by sequencing the promoter region of ilvC and by determining the factors affecting ilvY expression.